One unfortunate statistic has somewhat stifled the rollout and delivery of primarily Johnson and Johnson (J&J) and AstraZeneca vaccines. This statistic is what is known as the ‘efficacy rate’. Many have interpreted this as how effective the vaccine is at stopping you from getting COVID-19 and have consequently judged J&J and AstraZeneca to be ‘worse’ vaccines than Moderna or Pfizer due to their significantly lower ‘efficacy rates’. However, this is misguided. We can’t actually compare them to each other to measure effectiveness.
Based on recent studies, Moderna and Pfizer-BioNTech have efficacy rates of 94.1% and 95.3% respectively. This in numerical form appears significantly higher than J&J or AstraZeneca at 66.9% and 63% respectively. While this may easily be taken as the primary method for comparing the vaccines, it doesn’t show the whole picture.
To begin to understand why, we must look at how the efficacy rates are actually determined. The so called ‘efficacy rates’ are established through large scale clinical trials set out by each vaccine manufacturer in line with regulatory bodies. The clinical trials consist of two groups — half get vaccinated and half get the placebo. The trial participants are then sent back out into public to be monitored as to whether they contract COVID-19. For example, In the Pfizer trial, there were 43 000 participants, with 170 people ending up infected with the virus. Most importantly, how these people fall into the placebo versus vaccine category determines efficacy. If there were to be an equal number of participants who caught COVID-19 from placebo and vaccine groups, then efficacy would be 0%. On the other hand, if all 170 were from the placebo category and 0 from vaccine category, then the vaccine would have 100% efficacy. Ultimately, there was 162 in the placebo group and 8 in vaccine group — giving the Pfizer vaccine 95% efficacy. What this means is that a person with the vaccine is 95% less likely to get sick than a non vaccinated person if exposed to COVID-19.
The issue in comparing different trials lies in the disparities between when and where the trials were undertaken. For all of the vaccine manufacturers, their testing was performed at different times in different places — impacting on their efficacy rates. Moderna’s trial was done in the US in summer, when cases were still relatively low. Pfizer was done at a similar time, also in the US, whereas J&J’s trial took place in foreign countries such as Brazil and South Africa at a time when cases were spiking, with far more contagious variants including the Beta and Zeta variants. This means that it cannot be compared on equal standing to the other vaccine trials. Accordingly, you can’t study vaccine efficacy with the same inclusion criteria and controlled variables across all studies. Efficacy really just explains what happened in each trial not what will happen in the real world. Arguably, efficacy is not even the most important measure anyway. The goal of the vaccines is not necessarily to achieve ‘COVID 0’ (a complete elimination), but to remove its ability to kill or severely sicken. The most important thing is to stop people dying - and this is what EVERY vaccine does well. Not one fully vaccinated person in any of the trials was hospitalised or died due to COVID-19 as they are all highly effective in preventing hospitalisations and death. Efficacy matters but it doesn’t matter the most. With the Delta variant on the rise, the efficacy of vaccines will change, but not dramatically. Many recent studies have shown that Moderna and Pfizer vaccines still protect against Delta, though not as well as against previous variants.
Ultimately, the best vaccine is which ever one you are being offered. All of them will protect you from serious symptoms and death. Let’s bust this myth and get vaccinated.